This invention is related to methods and systems used to evaluate air void contents or characteristics of compacted materials used in the construction of roads, foundations, and other structures.
In recent years, design and use of open graded mixtures for the formation of paved roads have gained popularity. The term xe2x80x9copen-graded mixturesxe2x80x9d describes selections of mixed size compositions that can include various amounts of fine, medium, and coarse aggregates. When evaluating designs or performing quality control reviews or assessments of construction projects using open-graded mixtures, determining the air void content can be important because excessive air void content may be a precursor to the susceptibility of the roadway to have excessive water permeability that may, in turn, cause premature failure of the roadway. Thus, air void content is of concern in asphalt design and fabrication because it can provide an estimate of the mixtures"" stability and/or durability.
Conventionally, design evaluation criteria for a particular mixture is generally based upon several parameters including % air void content. In the past, to assess the % air void content, the maximum specific gravity of a loose mixture and the bulk specific gravity of a compacted representative sample of HMA (hot mix asphalt) is determined. As is known to those of skill in the art, the maximum specific gravity is typically evaluated using a method described in ASTM D2041. In the asphalt mix design industry, the % air voids (ASTM D3203) can be calculated for compacted mixtures using the determined bulk specific gravity (Gmb) and the maximum specific gravity (Gmm) values of the sample.
This % air void determination method assumes that the size distribution and composition of the compacted mixture at the site is uniform and similar to the distribution and composition of the mixture used in the evaluation test (i.e., the ASTM D2041 test). Therefore, an average Gmm value is presumed to be a good representation of the maximum specific gravity of the mixture used in the design and, ultimately, the construction project itself.
Using an average Gmm value may be a valid approach when dealing with fine, dense graded mixtures of HMA. The fine dense graded mixture can generally be suitably uniformly distributed and thus the sample Gmm is generally representative of that in the field site. In addition, any potential inhomogeneous distribution of small or fine grade aggregates in a compacted sample of same should not significantly influence the resultant quantification of the air void content because, typically, small aggregate grain densities are sufficiently close so as to not cause significant variations in the determined bulk specific gravity of compacted fine dense mixtures.
In contrast, with coarse and/or open graded mixtures, uniformly splitting the sample can be problematic. It is noted that the term xe2x80x9ccoarsexe2x80x9d is typically associated with aggregates retained on a 2.36 mm (No. 8) or larger sieve. In addition, it is oftentimes difficult to control the application of the open-grade mixture so as to obtain a substantially uniform distribution of the aggregate mixture in the field at the construction site when forming the roadway. Unfortunately, with coarse and/or open-grade mixtures, variation of large aggregate grains can significantly impact the bulk specific gravity (i.e., the Gmm and the Gmb values) of the sample. (See ASTM D2726 and D1188 for bulk specific gravity (Gmb) and ASTM D2041 for maximum specific gravity (Gmm), the contents of which are hereby incorporated by reference as if recited in full herein).
In view of the foregoing, there remains a need to provide air void content evaluation methods of open-graded and/or fine and/or coarse aggregate mixtures that can provide useful information about the potential life or durability of the resultant paved highway or roadway.
Embodiments of the present invention provide systems, methods, computer program products, and devices that can determine the porosity and/or effective air void content (xe2x80x9cEAVxe2x80x9d) of an open grade mixture comprising coarse or fine aggregates and/or combinations thereof. As described herein, the terms xe2x80x9cEAVxe2x80x9d and % porosity are used interchangeably as the same measure of the same parameter (porosity). In certain embodiments, the sample comprises compacted bituminous or asphalt material mixtures and the measurement is used to provide a measure or indicator of the permeability, stability and/or durability of a roadway formed from the mixture composition.
The EAV parameter determination can be carried out so as to selectively assess that portion of the voids in the sample that are accessible to water or other environmental liquids and/or fluids during service and to substantially disregard that portion of the voids that is not accessible to liquids and/or fluids (such as water) during service. That is, in service, generally stated, the air voids of particular interest are those that are accessible to fluid entry because it is these voids that can impact the durability of the construction project and/or that may indicate a propensity for excessive water permeability. The air voids that are not accessible to fluid entry (such as water and air) are less important to asphalt designers, but by obtaining the data for the EAV parameter, it is possible to calculate this inaccessible fraction of air voids by utilizing the measurement of % air voids which indicates the total amount of voids (both accessible and inaccessible). The EAV evaluation can be used to evaluate proposed designs of desired compacted samples including those employing open-grade mixtures. The EAV evaluation can also be used to perform quality control review of completed portions of paved roadways and similar construction projects to assure that certain standards have been met.
The EAV parameter can be represented as the percentage of water permeable voids in a compacted mixture. The EAV parameter can be calculated using a bulk specific gravity and an apparent maximum gravity of any desired compacted sample. In certain embodiments, the EAV measurement or evaluation can be directly performed and does not require the use of a Gmm value or a previously determined Gmm value that may not be representative of the gradation of a randomly selected compacted sample. The EAV parameter can be used as a direct indicator of mixture durability and/or stability and can strongly correlate to mixture permeability and/or segregation.
In certain embodiments, the evaluation can be carried out relatively swiftly, typically in under about 10 minutes (such as in about 7 minutes).
In certain embodiments, statistical variations in the EAV value(s) can be monitored and used to provide process control parameters during construction to assess the material composite mixture segregation. Alternatively or additionally, if the EAV value(s) is smaller than the % air void value, stripping potential may be identified as this comparison can indicate water absorption into the aggregates. It is also possible to determine the packing potential or % voids between aggregates by using the EAV value and % absorption of the aggregates.
Certain embodiments of the invention are directed to methods of determining the effective air void content of a compacted material sample. The method includes the steps of: (a) encasing a compacted material sample in a conformable sealant material (having a known or predetermined weight); (b) evacuating the encased material sample; (c) sealing the encased material specimen to provide a vacuum-sealed encased material sample; (d) obtaining the weight of the encased vacuum-sealed material sample in air; (e) immersing the vacuum-sealed encased material sample in a liquid displacement bath; (f) obtaining the weight of the sealant sample in the liquid bath; (g) introducing an opening into the sealant material of the encased material specimen while the material specimen and sealant material are held immersed in the liquid bath to allow liquid to enter the sealant material and contact the material sample; (h) obtaining the weight of the encased material sample during the immersing step after the introducing step; and (i) determining the porosity or effective air void content parameter value of the material sample based on the obtaining steps.
In particular embodiments, the method can include the step of calculating both the density of the vacuum sealed encased compacted material sample (xcfx811) and the density of the vacuum sealed sample after opening the seal under liquid (xcfx812). The determining step can also be carried out so as to include the step of calculating the effective air void content parameter value (EAV) using the mathematical equation:   EAV  =            (                                    ρ            ⁢            2                    -                      ρ            ⁢            1                                    ρ          ⁢          2                    )        xc3x97    100.  
Knowing EAV, the inaccessible air void content (percentage) can be calculated by the mathematical equation:
Inaccessible air voids=% air voidsxe2x88x92EAV. 
Other embodiments of the present invention are directed to alternative methods for determining the effective air void content of a compacted material sample. The methods can include: (a) determining the bulk specific gravity of the material sample (xcfx811); (b) drying a compacted material sample; (c) obtaining a dry weight of the material sample; (d) positioning the material sample in a rigid sealable container of known volume; (e) obtaining a first weight of the material sample and container under ambient pressure conditions; (f) evacuating the container to introduce a vacuum onto the material sample held therein; (g) introducing a known quantity of liquid into the container in a quantity sufficient to cover the material sample; (h) releasing the vacuum in the container with the material sample held immersed in the liquid; (i) obtaining the weight of the material sample in the open container in the liquid after the releasing step; j) calculating the maximum apparent density (xcfx812); and (k) determining the effective air void content of the compacted material sample undergoing analysis based on the obtained weights.
The bulk specific gravity of step (a) can be determined in any suitable manner. For example, using a sealing method as described in U.S. Pat. No. 6,321,589 (the contents of which are hereby incorporated by reference as if recited in full herein), using the method described in ASTM D1188, or using a dimensional evaluation methodology (mass/volume) as is known to those of skill in the art.
Still other embodiments of the present invention are directed to computer program products for determining the porosity and/or effective air void content of a compacted material sample undergoing analysis. The computer program product includes: (a) a computer readable storage medium having computer readable program code embodied in said medium, said computer-readable program code comprising: (b) computer readable program code for accepting input corresponding to a weight measurement of a vacuum sealed compacted material sample held encased in a sealant material; (c) computer readable program code for accepting input corresponding to a weight measurement of the encased material sample as it is held under liquid with the vacuum seal destroyed; (d) computer program code defining predetermined mathematical relationships for determining the effective air void content of the compacted material sample; and (e) computer readable program code for calculating the effective air void content of the compacted material sample undergoing analysis based on the weight measurements and the pre-determined mathematical relationships.
In certain embodiments, the program can also include computer readable program code for calculating both the density of the vacuum sealed encased compacted material sample (xcfx811) and the density of the vacuum sealed sample after opening the seal under liquid (xcfx812). In addition, the computer readable program code for calculating porosity or effective air void content can include the same mathematical equation noted above.
The effective air void content parameter is calculated and determined so as to be a measure of a subset of the air voids in the material sample. That is, the effective air void parameter corresponds to air voids in the compacted material that are accessible to liquids during service and substantially excludes or disregards air voids in the compacted material sample that are inaccessible to liquid during service.
However, by knowing EAV and % air voids (the % air voids can be evaluated using suitable methods such as that described in ASTM D3203), the percentage of inaccessible air voids can be calculated if desired.
The above summary is not intended to limit the scope of the invention as other apparatus, fixtures, operations, and computer programs can also be used to carry out the methods of the present invention.
The foregoing and other objects and aspects of the present invention are explained in detail in the specification set forth below.